Shade can equal lower electric bills

March 15, 2012 

A Marathon duplex gets a lot of shade from this tree, helping to keep the energy bill down.

BY LARRY KAHN

When it comes to energy in the Keys, solar can go both ways: You can install solar panels to power your home to reduce or eliminate your monthly electric bill -- or the sun can heat up your house so much that your bill is sky high.

Installing solar panels can be expensive and might not be an option. But with the right landscaping, you can reduce the impact of the sun's heat on your house and lower your bills.

Solar heat absorbed through windows and roofs can increase your air conditioner use. Incorporating shading concepts into your landscape can help reduce the solar heat gain, reducing your cooling costs.

Shading and evapotranspiration (the process by which a plant actively moves and releases water vapor) from trees can reduce surrounding air temperatures as much as 9 degrees. Because cool air settles near the ground, air temperatures directly under trees can be as much as 25 degrees cooler than air temperatures above nearby blacktop.

Using shade effectively requires you to know the size, shape and location of the moving shadow that your shading device casts.

Trees can be selected with appropriate sizes, densities and shapes for almost any shading application. To provide continuous shade or to block heavy winds, use dense trees or shrubs.

Trees with high, spreading crowns (i.e., leaves and branches) can be planted to the south of your home to provide maximum summertime roof shading. Trees with crowns lower to the ground are more appropriate to the west, where shade is needed from lower afternoon sun angles.

Although a slow-growing tree may require many years of growth before it shades your roof, it will generally live longer than a fast-growing tree. Also, because slow-growing trees often have deeper roots and stronger branches, they are less prone to breakage by windstorms. Slow-growing trees can also be more drought resistant than fast-growing trees.

A 6-foot to 8-foot tree planted near your home will begin shading windows the first year. Depending on the species and the home, the tree will shade the roof in five to 10 years.

Trees, shrubs and groundcover plants can also shade the ground and pavement around the home. This reduces heat radiation and cools the air before it reaches your home's walls and windows. Use a large bush or row of shrubs to shade a patio or driveway. Plant a hedge to shade a sidewalk. Build a trellis for climbing vines to shade a patio area.

Vines can also shade walls during their first growing season. A lattice or trellis with climbing vines, or a planter box with trailing vines, shades the home's perimeter while admitting cooling breezes to the shaded area.

Shrubs planted close to the house will fill in rapidly and begin shading walls and windows within a few years. However, avoid allowing dense foliage to grow immediately next to a home where wetness or continual humidity are problems.

Well-landscaped homes in wet areas allow winds to flow around the home, keeping the home and its surrounding soil reasonably dry.

This was provided by the U.S. Department of Energy.

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